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CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS
PRV SET
APPROX.
TO INLET VANE
69 kPa
ACTUATOR
BACK
COMPRESSOR
PRESSURE
TURBINE
CENTRIFUGAL
CHILLER
ABSORPTION CHILLER
CAPACITY CONTROL VALVE
PRESSURE
CONTROLLER
T2
P2
SENSING
ELEMENT IN
CONDENSER
DISCHARGE OF
WATER SUPPLY
ABSORPTION
TO ABSORBER
CHILLER
CONDENSER
WATER PUMP
Fig. 21. Schematic of Combination Absorption/
Centrifugal Chiller System Steam Piping
and Control Circuit.
CHILLER 1
CONDENSER
COMPRESSOR
EVAPORATOR
CENTRIFUGAL
CHILLER
CONDENSER
ABSORBER
EVAPORATOR
ABSORPTION
T1
CHILLER
Fig. 22. Schematic of Combination Absorption/
Centrifugal Chiller System Water Piping.
Figure 23 compares the steam consumption of individual
chillers to a combination system showing the savings using the
combination system. The range of centrifugal cutout points
indicates where most centrifugal chillers are shut down and the
absorption chiller provides all cooling required by the system.
HIGH PRESSURE
STEAM SUPPLY
T1
SENSOR IN
CHILLED
WATER
SUPPLY
RELAY
PRESSURE
ABSORPTION/
CONTROLLER
COMBINATION
P1
SELECTOR
SWITCH
ABSORPTION
CONDENSATE
CHILLER
RETURN
GENERATOR
TO
COOLING
CWR
TOWER
COOLING TOWER
C4085
BYPASS
V2
COOLING TOWER
BYPASS VALVE
COOLING
TOWER
P2
T2
C2689
2.375
2.250
2.125
2.000
TURBINE-DRIVEN
CENTRIFUGAL
CHILLER
1.875
1.750
1.625
1.500
1.375
15%
CENTRIFUGAL
CAPACITY
1.250
CENTRIFUGAL
1.125
CAPACITY
1.000
0.875
0.750
0.625
0.500
0.375
0.250
0.125
0
0
350
700
1050 1400 1750
Fig. 23. Typical Steam Consumption, Individual
and Combination Chillers.
CHILLER PUMP OPTIMIZATION
Pump configuration (variable water flow versus constant
water flow) also affects chiller system efficiency. Constant water
flow causes the largest change in efficiency from system no
load to design because the pump energy becomes a greater
percentage of the total energy input at light load conditions.
Variable water flow, using two-way load valves or variable speed
pumps, maintains the pump load at nearly a constant percentage
of the total energy input at all loads. If a chiller system has
constant water flow, chiller optimization must include pump
energy usage as part of the power calculation to account for
energy cost variations over the range of loads. In a chiller system
using variable water flow, it is not necessary to account for
pump energy cost. Refer to HOT AND CHILLED WATER
DISTRIBUTION SYSTEMS AND CONTROL.
ENGINEERING MANUAL OF AUTOMATIC CONTROL
314
ABSORPTION
CHILLER
25%
COMBINATION
SYSTEM
33%
SYSTEM
LOAD
18%
SYSTEM
LOAD
RANGE OF
CENTRIFUGAL
CUTOUT
2100 2450
2800
3150 3500
REFRIGERATION (KW)
C4086
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